In this study, researchers followed middle-aged, middle-class women living in Southern California for two decades in an effort to assess the impact of childbirth on later heart risk.

About half of the women died during the follow-up, and close to have of these women died of heart-related ailments or stroke.

Those who had given birth to four children or more were significantly less likely to die of heart disease or stroke than women who had not delivered children, even after accounting for the impact of other risk factors.

"These findings are reassuring because they do not show an increased [heart disease and stroke] risk later in life associated with pregnancy and delivery, but the protection associated with multiple deliveries was modest," Society for Reproductive Endocrinology and Infertility President Bradley Van Voorhis, MD, tells WebMD.

The study is published in the November issue of Fertility and Sterility.

Heart Disease in Women

Heart disease is the leading killer of women in the U.S., with more than 300,000 deaths occurring each year.

The study included close to 1,300 women who were age 50 and older when they had their first clinic visit as study participants in the mid-1980s.

The women were asked about their reproductive histories, including the number of pregnancies they had lasting three months or more, the number of babies they gave birth to, and their menopausal histories and use of estrogen therapy.

They were also interviewed to determine their individual risk factors for heart disease.

The average woman who participated in the study had a history of two pregnancies and live births, but some women had no biological children and at least one woman had 13 children.

Compared to women who had not given birth, giving birth to four or more children was associated with a modest decrease in deaths overall from heart disease and stroke, with the strongest association seen for deaths from stroke.